1. Field of the Invention
The present invention generally relates to charged-particle-beam exposure devices and methods for using such devices, and particularly relates to a charged-particle-beam exposure device and a charged-particle-beam exposure method of a multi-beam-blanking-aperture-array type having a plurality of rectangular apertures and electrodes arranged in proximities thereof for deflecting a plurality of beams.
Integrated circuits (IC), with recent developments in functions and circuit density, have been playing an important role as a core technology for technological development in industrial fields such as computers, telecommunications, mechanical control, etc. Circuit density of ICs has been on a rapid increase, quadrupling every two to three years. Such a rapid increase in the circuit density is achieved based on developments in micro-process technology.
2. Description of the Related Art
A block exposure method and a blanking-apperture-array (BAA) exposure method, which have been recently proposed as micro-process technology, can achieve as high a throughput as 1 cm.sup.2 /sec. These two methods are known to be superior compared to other micro-process technology in terms of the fineness of the process, the exposure positioning accuracy, the turn-around speed, and reliability.
FIG. 1 is an illustrative drawing showing a blanking aperture array used in a BAA exposure device. The blanking aperture array includes a plurality of rectangular apertures and electrodes arranged in proximities of the apertures for deflecting beams. Voltage is separately applied to each of the electrodes via wiring to individually control the deflection of a charged-particle beam passing through a corresponding aperture. The charged-particle beam deflected by the voltage applied to the electrode can be blanked by a diaphragm located downstream with respect to the beam flow, so that a micro beam can be switched, between on and off states on an exposed wafer. At the time of an exposure process, all apertures as shown in FIG. 1 are exposed to a charged-particle beam, and a number of micro beams passing through the apertures are directed to the wafer. By applying appropriate voltages to the electrodes, the micro beams can be switched between on and off states, selectively and thus independently of each other.
A charged-particle-beam exposure device includes a first deflector (main deflector: electromagnetic deflector) for deflecting a charged-particle beam by a large magnitude, and a second deflector (sub-deflector: static-charge deflector) for deflecting the charged-particle beam by a fine magnitude. A set of the micro beams exposed onto the wafer, while being switched between on and off states, are deflected by the second deflector to draw a required pattern on the wafer. At the same time, the wafer is moved in a certain direction (X direction) by a wafer stage. The pattern is drawn by deflecting and scanning the set of the micro beams in the Y direction faster than the movement of the wafer stage in the X-direction.
FIG. 2 is an illustrative drawing showing an exposure area for pattern drawing. As shown in the figure, an area having a 2-mm width is divided into 100-.mu.m square areas. Each of the 100-.mu.m square areas is further divided into 10-.mu.m-by-100-.mu.m stripe areas, which are called cell stripes. An interior of a cell stripe is drawn by the set of the micro beams scanned in the Y direction as described above. After finishing the drawing in a given cell stripe, the set of the micro beams is deflected in an X direction to an adjacent cell stripe by the second deflector and, then, an interior of the latter cell stripe is drawn by the Y-direction scanning.
An area size covered by the second-deflector deflection is about 100 .mu.m in the X direction. After finishing the drawing in a given 100-.mu.m square area, the set of the micro beams is shifted to an adjacent 100-.mu.m square area. Then, the drawing on the wafer continues in the same manner.
In the example of FIG. 1, the apertures are arranged in 8 lines including a first line A, a second line B, a third line C, . . . , and an eighth line H. Each line is comprised of two sub-lines. For example, the line A is comprised of a sub-line A1 and a sub-line A2. In order to draw a pattern without any pattern gaps, the apertures in one sub-line are staggered with the apertures in the other sub-line to fill the pattern gaps. Thus, in principle, two sub-lines constitute one line. Each line includes 64 apertures.
The lines A through H are divided into four sets K.sub.1 through K.sub.4, with two adjacent lines forming a respective set. Among the two lines in a given set (e.g., the line A and the line B in the set K.sub.1), apertures in the first line (e.g., the line A) allow passage of micro beams directed to given positions on the wafer, and, then, apertures in the second line (e.g., the line B) allow passages of micro beams scanned in the Y direction to be exposed to the same positions on the wafer. In this manner, the two lines in the same set are used for exposing the micro beams to the same positions on the wafer to ensure reliable drawing.
The four sets K.sub.1 through K.sub.4 are staggered in the X direction and in the Y direction with each other, so that the micro beams of these sets are superimposed by half the beam size on the wafer. FIG. 3 is an illustrative drawing showing the superimposition of the micro beams. As shown in FIG. 3, each micro beam is arranged at intervals of half the beam size (i.e., high pitch), so that a fine adjustment of the pattern-edge drawing, a closing-effect correction, etc., can be carried out at a higher precision than the beam size itself.
FIG. 4 is a block diagram of a BAA exposure system. In FIG. 4, the charged-particle-beam exposure device includes an exposure-column unit and a control unit. The exposure-column unit includes a charged-particle-beam generator 200, a lens 201 for converging the charged-particle beam, a BAA 202, a blanking aperture 203 for blanking or passing the beams according to a blanking signal, a round aperture 204 for blanking the beams, a lens 205 for converging the beams, a refocus coil 206 for correcting an increase in the beam focus distance, a dynamic-stigmator coil 207, a dynamic-focus coil 208, and a main deflector 209 and a sub-deflector 210 for positioning the beams on the wafer. The exposure-column unit further includes a stage 211 movable in the X and Y directions for carrying the wafer.
The control unit includes a CPU 100 responsible for control of the entire system of the charged-particle-beam device. The control unit further includes an SEM/MD-control unit 101 responsible for control at the time of the mark detection and SEM, an exposure-management unit 102, a BAA-management unit 103, a shooting memory 105 for storing BAA data, a refocus memory 108 for storing refocus data, a main-deflector-deflection-amount setting unit 109, a sub-deflector-deflection-amount setting unit 112, and a stage controlling unit 113, all of which are connected with each other and with the CPU 100 via a data bus such as the VME bus. The control unit further includes a conversion/amplification unit 106 for applying parallel-to-serial conversion and amplification to the data from the shooting memory 105, a stigmator-coil driving unit 110, a refocus-coil driving unit 111, and a loader-management unit 114.
The CPU 100 is connected with a data-management CPU 120 for data management. The data-management CPU 120 is connected via a data bus with a disk 121 for storing pattern data, a data-expansion unit 122 for expanding the pattern data into bit-map data, a bit-map-data disk 104 for storing the bit-map data, and a refocus-data disk 107 for storing refocus data. The refocus data is used for correcting an increase in the beam focus distance, and is generated by the data-expansion unit 122.
In FIG. 4, the pattern data generated from design data is supplied from the disk 121 to the data-expansion unit 122, which expands the supplied data into the bit-map data. The bit-map data is stored in the bit-map-data disk 104 for each cell stripe or for each set of cell stripes. Also, the refocus data is generated from the bit-map data, and is stored in the refocus-data disk 107.
The data-expansion process described above is carried out prior to the exposure process, so that the data-expansion process does not impose any restriction on the speed of the exposure-process. Also, once the data is expanded, another data-expansion process is no longer necessary and the same expanded data can be used, as long as the same pattern is to be exposed.
The bit-map data is transferred from the bitmap-data disk 104 to the shooting memory (high-through-put buffer) 105. The shooting memory 105 has a capacity to store data for two 20-mm square chips. When the chip size to be exposed in smaller than a 20-mm square, the shooting memory 105 can be divided into two, with one used for data output and the other used for data storage. In this manner, the data storage and the data output can be simultaneously carried out. That is, while a given chip is exposed, data for the next chip can be stored. When the chip size to be exposed is larger than a 20-mm square, either the data storage or the data output is carried out exclusively.
The data from the shooting memory 105 is supplied to the conversion/amplification unit 106. The conversion/amplification unit 106 applies the parallel-to-serial conversion to the supplied data and manages the timing control, and, also, amplifies the data to supply it to the BAA 202.
At the time of the exposure, the main-deflector-deflection-amount setting unit 109 and the sub-deflector-deflection-amount setting unit 112 define the deflection amounts of the main deflector 209 and the sub-deflector 210, respectively, and the sub-deflector 210 starts the scan. At the same time, a signal indicating a start of a cell-stripe exposure is supplied to the BAA-management unit 103. In response, data defining on/off states of each micro beam for one cell stripe is supplied to the BAA 202 under the control of the BAA-management unit 103.
The BAA-type exposure device described above can be used for exposing any of various types of patterns without sacrificing the throughput or production. Since it requires a large amount of data at the time of exposure, however, a high-speed data output becomes necessary in order to draw fine patterns at high throughput or production levels. As described above, in the related-art device and the method, the data is supplied to the BAA 202 in the following procedure.
1. The pattern data is expanded by the data-expansion unit 122 to generate the bit-map data and store it in the bit-map-data disk 104.
2. The required exposure data is transferred from the bit-map-data disk 104 to the shooting memory 105.
3. The data is output in parallel from the shooting memory 105 at the time of exposure.
4. The output data is subjected to processing by parallel-to-serial conversion unit and amplification unit 106, and then is supplied to the BAA 202.
The shooting memory 105 requires a large capacity, and, thus, needs to be comprised of a DRAM. Since the memory data length is 16 bits, a data serial output is only 160 MHz at a maximum, even when the data is output at 100 nsec intervals. Thus, even if other units have sufficient capacity for a high-speed exposure process, production is restricted by the serial output of 160 MHz. This cap on production cannot be exceeded.
In order to obviate this problem, the high-speed page mode of the DRAM may be used to boost the memory access speed. Different from a normal mode requiring successive inputs of row addresses and column addresses, the high-speed page mode allows continuous inputs of column addresses for one row-address input to achieve a high-speed-data-read operation. Therefore, use of this high-speed page mode in the shooting memory 105 should achieve a high-speed-data-read operation to boost production.
However, column addresses in the memory are comprised of 256 addresses, for example, so that continuous data reading can be made only for 256 addresses. If the column address to be read exceeds a 256th address, a page-hit error is generated, stopping the data-read operation. Namely, data for only 256 addresses can be subjected to the continuous data reading, and the data-read operation is temporarily stopped when a next row address is accessed after accesses to the 256 column addresses.
If such a temporal stoppage of the data-read operation occurs during a cell-stripe exposure, the exposure process is forced to stop, impairing the cell-stripe exposure.
Accordingly, there is a problem in the BAA-type charged-particle-beam exposure device and method in that the data-read operation is forced to stop, impairing the exposure process when the high-speed-data-read operation is used for boosting production.
Accordingly, there is a need for a BAA-type charged-particle-beam exposure device and a method therefor which can read out data without impairing the exposure process when the high-speed-data-read operation is used for boosting the throughput.